BACKGROUND OF THE INVENTION
Field of the Invention
[0001] The present invention relates to an impact resistant structure for a helicopter and
an energy absorber used for the same.
Description of the Related Art
[0002] A helicopter is often operated in visual flight rule, or between mountains, or at
a low altitude, because of its operating characteristics. Then, there is always a
risk of accident due to contact with an obstacle. Therefore, an impact resistance
is strongly required in a helicopter in order to keep survivability of crew members
in the crash situations.
[0003] The basic principle for the impact resistant structure of a helicopter is to adopt
a continuous strong keel K for a nose H easily crushed and a bottom G easily crushed
which are shown in Fig. 16(a) to prevent a floor D from structural failure on crash
landing as shown in Fig. 16 (b) , to adopt a strong outer skin P as shown in Fig.
16(c), to adopt a strong beam B on the keel K, and to adopt a continuous strong frame
F.
[0004] For a helicopter of which landing gear, such as retracted one, may not be effectively
functioned for crash energy absorption, an impact resistant fuselage structure having
impact absorption capacity is required for the typical crush environment shown in
Fig. 17 in a shape fitting to the actual helicopter fuselage structure.
[0005] Conventionally, the floor structure of a helicopter is designed according to a normal
operational flight load and a landing load on the ground. At present, general impact
absorption to an unexpected crash impact like crushing shown in Fig. 17 is not taken
into account.
[0006] Conventional impact resistant structures for the helicopter are disclosed in USP
No.4593870, USP No.5069318, and USP No.5024399. Meanwhile, in a helicopter, on the
typical ground surface, as shown in Fig. 18, the ground reaction force is concentrated
on the outer wall, though in the impact resistant structures disclosed in the above-mentioned
US patents, a floor member is not arranged so as to be suitable to ground reaction
force. Further, as shown in Fig. 19 (Ref. "Full-Scale Crash Test of the Sikorsky Advanced
Composite Airframe Program Helicopter" Richard L. Botinott, AHS 56
th), the web intersection part X is hard to be crushed, and the sub-floor effective
stroke is not effectively utilized, so that a sufficient floor acceleration reduction
is not realized. Furthermore, the effective function, under the condition in which
the landing gear is not effectively functioned, against the combined crash speed environment
of the horizontal speed and drop speed of the general crash environment of a helicopter
shown in Fig. 17 is not disclosed in the US patents.
[0007] Examples of impact resistance absorption members used in the impact resistant structure
of a helicopter and the impact resistant structure for general industrial purpose
are disclosed in Japanese Patent Laid-Open Publications No.2002-286066, No.2002-36413,
No.2002-153169, No.2002-192432, and USP No.5746537, such as an example using axial
compression energy absorption of a light weight fiber reinforced composite material
tube, and an example that a foaming material is filled up in all sections for energy
absorption improvement.
[0008] However, to reduce an impact load by a long absorption stroke, and simultaneously,
to realize high impact energy absorption of the merit of a fiber reinforced composite
material tube without instability of overall general buckling, if the section of the
single tube is simply made larger, the local buckling tendency of the tube wall will
be increased and the stable progressive failure mode suitable for impact energy absorption
of fiber reinforced composite tube shown in Fig. 20 cannot be achieved. Further, when
a foaming material is filled in all the sections, a space for releasing destroyed
small pieces of the composite material generated in the progressive failure mode is
lost, and the destroyed small pieces are compacted, and the energy absorber will become
extremely stiffened. Thereby, the effective stroke is reduced, and a required impact
absorption capability is not obtained. Further, to reduce the local unstable buckling
of the tube wall, when the section size of the tube is made compact, the aspect ratio
(energy absorber height/ section width) of whole the energy absorber becomes long
and slim, and the energy absorber becomes weak for bending and eccentric compression,
so a desired axial compression energy absorption property cannot be achieved. As a
solution for these problems, when the section of the tube is made compact, and is
made into a bundling shape, when the number of tubes is optionally adjusted, the number
of intersections between stiff walls increases as the number of tubes increases, so
that as shown in Fig.21, the initial load peak level harmful for the impact absorption
property increases.
SUMMARY OF THE INVENTION
[0009] Therefore, an object of the present invention is to provide an impact resistant structure
of a helicopter, i.e., for a helicopter of which landing gear such as retracted one
may not be effectively functioned in crash situation, to provide a fuselage structure
having impact absorption capacity against the actual crash environment while providing
in a shape fitting to the actual helicopter fuselage structure. Another object of
the present invention is to provide a light weight energy high performance absorber
in which the harmful initial load peak level is reduced, and in which the energy absorption
property due to axial compression failure is improved, also which is able to apply
not only to the impact resistant structure of a helicopter but also to the impact
resistant structure for general industrial purpose, and which have a desired impact
absorption capacity in a shape fitting to the actual helicopter fuselage structure,
furthermore in which the effective stroke is increased.
[0010] According to one aspect of the present invention, an impact resistant structure of
a helicopter comprises: an energy absorber positioned under a floor of the helicopter
and directly connected to a frame of the helicopter, the energy absorber being arranged
in accordance with a distribution of a ground reaction force on a general ground surface
at a time of crash situation.
[0011] According to another aspect of the present invention, an impact resistant structure
of a helicopter comprises: an energy absorber in bundled-tubes state directly connected
to a frame of the helicopter at a position almost directly under the frame where an
impact load is concentrated at a time of crash situation.
[0012] Preferably, the impact resistant structure of a helicopter further comprises a plurality
of curved panels, which take a horizontal load due to a forward crash speed and are
crushed in a pantograph shape by a vertical load at the time of crash situation, arranged
almost in an longitudinal direction of the helicopter and connected to an under-floor
outer skin or web of the helicopter.
[0013] Preferably, an impact resistant structure of a helicopter further comprises a truss
frame connecting the curved panels almost in an X-shape so as to function as a frame
member for holding the curved panels during a normal operational use and not to prevent
the curved panels from deforming in the pantograph shape at the time of crash situation.
[0014] Preferably, in the impact resistant structure of a helicopter, a floor beam of the
helicopter is arranged on the curved panels, the floor beam being connected to the
frame to which the energy absorber is directly connected, thereby a frame-floor beam
structure is formed.
[0015] Preferably, in the impact resistant structure of a helicopter, a cabin structure
in a gate shape is positioned above the frame-floor beam structure, the cabin structure
being connected to the frame-floor beam structures at both side ends of the frame.
[0016] According to another aspect of the present invention, an energy absorber comprises:
a plurality of independent hollow tubes of fiber reinforced composite material integrally
formed by bundling only the hollow tubes of fiber reinforced composite material, the
hollow tubes of fiber reinforced composite material being arranged to reduce a number
of intersections between walls of the hollow tubes.
[0017] According to another aspect of the present invention, an energy absorber comprises:
a plurality of independent hollow tubes of fiber reinforced composite material bundled
by an outer layer of fiber reinforced composite material, wherein the hollow tubes
of fiber reinforced composite material and the outer layer of fiber reinforced composite
material are arranged so as to reduce a number of intersections between walls of the
hollow tubes or between the wall of the hollow tube and the outer layer.
[0018] Preferably, in the energy absorber, the hollow tubes of fiber reinforced composite
material and the outer layer of fiber reinforced composite material are arranged such
that a number of intersecting walls of the hollow tubes or the outer layer is less
than four surfaces.
[0019] Preferably, in the energy absorber, the hollow tubes of fiber reinforced composite
material and/or the outer layer of fiber reinforced composite material for bundling
the hollow tubes are formed in a plurality of layers in a thickness direction, a film-shaped
layer material having lower strength than that of a base material being inserted between
end portions of the plurality of layers.
[0020] Preferably, in the energy absorber, the hollow tubes of fiber reinforced composite
material and the outer layer of fiber reinforced composite material for bundling the
hollow tubes are integrally formed.
[0021] Preferably, in the energy absorber, a foaming material is inserted into a properly
selected space from between the hollow tubes of fiber reinforced composite material,
between the hollow tubes of fiber reinforced composite material and the outer layer
of fiber reinforced composite material, and insides of the hollow tubes of fiber reinforced
composite material.
[0022] Preferably, in the energy absorber, the hollow tubes of fiber reinforced composite
material are provided with a sectional space for storing destroyed small pieces sequentially
generated by progressive crushing.
[0023] Preferably, in the energy absorber, a sectional shape of each of the hollow tubes
of fiber reinforced composite material is circular, elliptic, square, triangular,
hexagonal, or octagonal.
[0024] Preferably, in the energy absorber, the hollow tubes of fiber reinforced composite
material are arranged in a row or in plural rows and are bundled circularly, elliptically,
rectangularly, or squarely by the outer layer of fiber reinforced composite material.
[0025] Preferably, in the energy absorber, the hollow tubes of fiber reinforced composite
material, the foaming material, and the outer layer of fiber reinforced composite
material are integrally formed.
BRIEF DESCRIPTION OF THE DRAWINGS
[0026] The above and other objects, features and advantages of the present invention will
become more apparent from the following description taken in connection with the accompanying
drawings, in which:
Fig. 1 is a schematic perspective view showing the bone structure of the sub-floor
of a helicopter to which the impact resistant structure of an embodiment of the present
invention is applied;
Fig. 2 is an enlarged perspective view of the section A shown in Fig. 1;
Fig. 3 is an enlarged perspective view of the section B shown in Fig. 1;
Fig. 4 is a perspective view showing an example of the gate-shape structure formed
on the frame-floor beam structure of the impact resistant structure of the embodiment
of the present invention;
Fig. 5 is a perspective view showing one of the energy absorbers of the embodiment
of the present invention;
Fig. 6 is a perspective view showing a partially modified example of the energy absorber
shown in Fig. 5;
Fig. 7 is a perspective view showing another example of the energy absorbers of the
embodiment of the present invention;
Fig. 8 is a drawing showing other examples of the sectional shapes of the hollow tubes
of fiber reinforced composite material of the energy absorbers of the embodiment of
the present invention;
Fig. 9 is a drawing showing examples of bundling arrangement of the hollow tubes of
fiber reinforced composite material each having an octagonal section;
Fig. 10 is a drawing showing various examples of the energy absorbers of the embodiment
of the present invention, in which a foaming material is inserted into hollow tubes
of fiber reinforced composite material having the same circular section, square section,
and octagonal section which are bundled and arranged by an outer layer made of fiber
reinforced composite material;
Fig. 11 is a drawing showing the configuration of energy absorbers of the conventional
example and the configuration of energy absorbers of Embodiments 1 and 2 for which
the load-displacement characteristic test for measuring the initial load peak is to
be carried out;
Fig. 12 is a graph showing the results of the load-displacement characteristic test
of the energy absorbers of the conventional example and Embodiments 1 and 2 shown
in Fig. 11;
Fig. 13 is a perspective view showing an energy absorber of the embodiment and energy
absorbers of conventional Examples 1 and 2 for which the impact energy absorption
property is to be measured;
Fig. 14 is a graph showing the measured results of the energy absorption property
of the energy absorber of the embodiment and energy absorbers of Conventional Examples
1 and 2 shown in Fig. 13;
Fig. 15 is a graph showing the existence of the effective stroke by the load-displacement
characteristic test of the energy absorbers of the conventional example and the energy
absorbers of Embodiments 1 and 2;
Fig. 16 is a drawing for explaining the basic principle of the impact resistant structure
of a helicopter, (a) is a schematic vertical sectional side view of the helicopter
on the nose side, (b) is a schematic side view on the nose side at the time of crash
situation, and (c) is a schematic vertical sectional view of the fuselage;
Fig. 17 is a drawing showing the general crush environment of a helicopter;
Fig. 18 is a drawing showing the state that the under-floor crush load on the general
ground surface is concentrated on the outer wall;
Fig. 19 is a perspective view showing the crushing state of the floor member of a
conventional helicopter;
Fig. 20 is a drawing showing the preferable and stable sequential destruction mode
for impact energy absorption intrinsic to tubes of composite material; and
Fig. 21 is a drawing showing the general load-displacement characteristics of tubes
of composite material at the time of crushing in the axial direction.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0027] An impact resistant structure for the helicopter of an embodiment of the present
invention and an energy absorber of an embodiment of the present invention used in
the same will be explained below with reference to the accompanying drawings.
[0028] Firstly, the impact resistant structure of a helicopter will be explained by referring
to Figs. 1 to 3. The gray parts shown in Fig. 1 are energy absorbers 1 in bundled-tubes
state. The energy absorbers 1 are arranged under the floor in accordance with the
ground reaction force distribution at the time of crash situation on the general ground
surface shown in Fig. 17 and are directly connected to a frame 2 as shown in Figs.
2 and 3.
[0029] The energy absorbers 1 in the bundled-tubes state may be directly connected to the
frame 2 almost directly under the side wall of the frame 2 where the impact load is
concentrated at the time of crash situation shown in Fig. 17. In Fig. 1, numeral 3
indicates an under-floor outer skin or web and on the under-floor outer skin or web
3, many curved panels 4 are arranged integrally and in parallel with each other almost
in the longitudinal direction of the helicopter. The curved panels 4 operate as a
keel beam during the normal operational use as shown in Figs. 2 and 3, receive the
horizontal load due to the forward speed at the time of crash situation shown in Fig.
17, and are crushed in a pantograph shape by the vertical load.
[0030] Between the curved panels 4, a truss frame 5 is installed in an almost X shape as
shown in Fig. 2. The truss frame 5 holds the curved panels during the normal operational
use. The truss frame 5 does not prevent the curved panels 4 from deformation at the
time of crushing. A floor beam 6 is arranged on the curved panels 4. The floor beam
6 is connected to the frame 2, to which the energy absorbers 1 are directly connected,
as shown in Fig. 2, thereby, a frame-floor beam structure 7 is formed.
[0031] In the impact resistant structure of a helicopter of the present embodiment which
is configured as described above, the energy absorbers 1 in the bundled-tubes state
are arranged under the floor in accordance with the ground reaction force distribution
at the time of crash situation on the general ground surface and are directly connected
to the frame 2. Thereby, even if the under-floor crush load is concentrated on the
outer wall, the energy of crash is absorbed stably by the energy absorbers 1 in the
bundled-tubes state which is excellent in energy absorption per unit weight.
[0032] Further, on the sub-floor outer skin or web 3, many curved panels 4 which operate
as a keel beam during the normal operational use, receive the horizontal load due
to the forward crash speed at the time of crash situation, and are crushed in a pantograph
shape by the vertical load, and are arranged integrally and in parallel with each
other almost in the longitudinal direction of the structure. Thereby, the under-floor
stroke S is reserved and effectively used at the time of crash situation and the floor
surface acceleration is sufficiently reduced.
[0033] Moreover, the truss frame 5 is installed between the curved panels 4, so that the
truss frame 5, during the normal operational use, functions as a frame member for
holding the curved panels 4, and at the time of crash situation, the curved panels
4 are surely crushed in a pantograph shape without preventing deformation, and the
crash impact absorption capacity of sub-floor is improved.
[0034] Furthermore, since the floor beam 6 arranged on the curved panels 4 is connected
to the frame 2 to which the energy absorbers 1 in the bundled-tubes state is directly
connected so that the frame-floor beam structure 7 is formed, a gate-shape cabin structure
8 connected to the frame 2 at both side ends as shown in Fig. 4 can be formed above
the frame-floor beam structure 7. During the normal operational use, the cabin structure
8 is supported by the frame-floor beam structure 7, and at the time of crash situation,
the frame-floor beam structure 7 is prevented from destruction because the impact
is absorbed by the energy absorbers 1 in the bundled-tubes state and the curved panels
4. Thereby, the cabin structure 8 is also prevented from destruction, and a crew member's
survivable volume 9 inside the cabin structure 8 is maintained, and the survivability
of crew members is improved. Moreover, the cabin structure 8 is a crew member's protective
shell structure for preventing heavy equipments, e.g., a transmission, engine, etc.,
on the ceiling from falling or intrusion into the cabin at the time of crash situation
and thereby the crew member's survivable volume is reserved.
[0035] Next, the energy absorbers 1 of the present embodiment used in the aforementioned
impact resistant structure of a helicopter will be explained by referring to the drawings.
Basically, with respect to the energy absorbers 1, it is desirable to bundle a plurality
of hollow tubes of fiber reinforced composite material, reduce the number of intersecting
walls of the hollow tubes of fiber reinforced composite material, and integrally form
them. However, one unlimited example of the energy absorbers 1 is that as shown in
Fig. 5, a plurality of independent hollow tubes of fiber reinforced composite material
10 having a small opening section are bundled by an outer layer made of fiber reinforced
composite material 11, thus the walls of the hollow tubes of fiber reinforced composite
material 10 which are light weight and excellent in energy absorption are stabilized
from local buckling.
[0036] In the energy absorbers 1, when the number of intersections of the walls of the hollow
tubes of fiber reinforced composite material 10 is reduced and the number of intersecting
walls of the hollow tubes of fiber reinforced composite material 10 or outer layer
made of fiber reinforced composite material 11 is reduced, the intersections are prevented
from stiffening and the harmful initial load peak for crew member's survivability
is suppressed.
[0037] Particularly, the hollow tubes of fiber reinforced composite material 10 and the
outer layer made of fiber reinforced composite material 11 for bundling them are arranged
such that a number of intersecting walls of the hollow tubes or outer layer is less
than four surfaces. Thereby, the harmful initial load peak for crew member's survivability
is suppressed more.
[0038] Further, when the outer layer made of fiber reinforced composite material 11, as
shown in Fig. 6, is formed in a plurality of layers in the thickness direction and
between end portions 12 of the outer layer 11, a film-shaped layer material of low
strength, for example, delamination films 13 are inserted, the harmful initial load
peak for crew member's survivability is suppressed more. Further, in the energy absorbers
1, when the hollow tubes of fiber reinforced composite material 10 and the outer layer
made of fiber reinforced composite material 11 for bundling them are integrally formed,
energy of crush is preferably absorbed stably.
[0039] Another example of the energy absorber 1 of the present embodiment is that as shown
in Fig. 7, in the space between the hollow tubes of fiber reinforced composite material
10 and in the space between the hollow tubes of fiber reinforced composite material
10 and the outer layer made of fiber reinforced composite material 11 for bundling
the tubes, a foaming material 14 is inserted. Thereby, the walls of the hollow tubes
of fiber reinforced composite material 10 are more stabilized from local buckling.
[0040] Further, the foaming material 14 is inserted not only into the space between the
hollow tubes of fiber reinforced composite material 10 and into the space between
the hollow tubes of fiber reinforced composite material 10 and the outer layer made
of fiber reinforced composite material 11 but also properly selected insides of the
hollow tubes of fiber reinforced composite material 10.
[0041] Further, the hollow tubes of fiber reinforced composite material 10 are provided
with a sectional space 15 for storing destroyed small pieces sequentially generated
by progressive crushing, so that whole energy absorber is prevented from stiffening
due to compacting of the destroyed small pieces.
[0042] And, in the energy absorbers 1 shown in Fig. 7, when the hollow tubes of fiber reinforced
composite material 10, the foaming material 14, and the outer layer made of fiber
reinforced composite material 11 for bundling the tubes are integrally formed, the
strength for bending and eccentric compression can be obtained and energy of crash
can be absorbed stably.
[0043] In the energy absorbers 1 of the present embodiment, the sectional shape of each
of the hollow tubes of fiber reinforced composite material 10 shown in the drawing
is octagonal. However, as shown in Fig. 8, it may be circular, elliptic, square, triangular,
or hexagonal. Further, as shown in Fig. 9, the hollow tubes of fiber reinforced composite
material 10 having, for example, an octagonal section, may be arranged in a row, two
rows, or three rows and bundled by the outer layer made of fiber reinforced composite
material 11 rectangularly, squarely, circularly, or elliptically.
[0044] Furthermore, as shown in Fig. 10, the hollow tubes of fiber reinforced composite
material 10 and the foaming material 14 may have the same sectional shape of circle,
square, or octagon and may be bundled and arranged by the outer layer made of fiber
reinforced composite material 11. In this case, it is also preferable that the foaming
material is inserted into the hollow tubes of fiber reinforced composite material
10 and has the same sectional shape as that of the hollow tubes of fiber reinforced
composite material 10.
[0045] In the energy absorbers 1 of the present embodiment, the hollow tubes of fiber reinforced
composite material 10 are composed of fibers and hollow tubes of fiber reinforced
composite material of resin, and as fibers, fibers of glass, carbon, alamide, metal,
or boron and conjugate fibers are selectively used, and as resin, thermoset resin
and thermoplastics are selectively used. For the foaming material 14, various materials
such as polyethylene series, polyurethane series, polystyrene series, epoxy resin
series, phenolic resin series, and polymethacrylic imide series are selectively used.
[0046] To make the initial load peak suppression effects by the energy absorbers 1 of the
present embodiment clear, the load-displacement characteristic test is carried out
on an energy absorber of the conventional example and energy absorbers of Embodiments
1 and 2.
[0047] The configuration of the energy absorbers of the conventional example and the configurations
of the energy absorbers of Embodiments 1 and 2 are shown in Fig. 11 and the results
of the load-displacement characteristic test of the energy absorbers are shown in
the graphs in Fig. 12. In the energy absorber of the conventional example, the initial
load peak harmful for the impact absorption property is extremely large, while in
the energy absorber of Embodiment 1, the initial load peak is extremely suppressed
and in the energy absorber of Embodiment 2, the initial load peak is eliminated.
[0048] Further, to make the initial load peak suppression effects by the energy absorbers
1 of the present embodiment clear, the energy absorption property per unit mass of
the energy absorber of the embodiment shown in Fig. 13 and the energy absorber of
Conventional Examples 1 and 2 is measured. The graph in Fig. 14 shows that the energy
absorber of the embodiment has an extremely high impact energy absorption property
compared with the energy absorbers of Conventional Examples 1 and 2.
[0049] Furthermore, to make the effects of the energy absorbers of the present embodiment
on the effective stroke clear, on a conventional energy absorber, an energy absorber
having no sectional space by filling of the foaming material of Embodiment 1, and
an energy absorber having a sectional space of Embodiment 2, a load-displacement characteristic
test is carried out.
[0050] The graphs in Fig. 15 show that in the energy absorber of the conventional example,
the effective stroke is not used effectively due to unstable destruction, thus energy
cannot be absorbed. On the other hand, in the energy absorber of Embodiment 1, destroyed
small pieces are cut into the foaming material, thus the member as a whole is prevented
from stiffening due to compacting of the destroyed small pieces, and the effective
stroke is sufficiently used. Moreover, in the energy absorber of Embodiment 2, destroyed
small pieces are stored in the sectional space, thus the member as a whole is prevented
from stiffening due to compacting of the destroyed small pieces, and the effective
stroke is sufficiently used.
[0051] As mentioned above, the impact resistant structure of a helicopter, e.g., a helicopter
of which landing gear such as retracted one may not be effectively functioned, of
the present invention can produce an excellent effect that the fuselage structure
can be provided with impact absorption capacity against the actual crash environment
in a shape fitting to the actual helicopter fuselage structure.
[0052] Further, the energy absorber of the present invention can suppress the harmful initial
load peak for crew member's survivability, improve the absorption property of compression
crush energy, and increase the effective stroke, so that they can be applied not only
to the impact resistant structure of a helicopter but also to the impact resistant
structure for general industrial purpose and can provide a desired impact absorption
capacity in a shape fitting to the actual helicopter fuselage structure.
[0053] Although the invention has been described in its preferred embodiments with a certain
degree of particularity, obviously many changes and variations are possible therein.
It is therefore to be understood that the present invention may be practiced otherwise
than as specifically described herein without departing from the scope and spirit
thereof.
1. An impact resistant structure of a helicopter, comprising: an energy absorber formed
of a bundle of tubes directly connected to a cabin frame of said helicopter at a position
substantially under a side wall of said frame, at which position an impact load is
concentrated in the event of a crash.
2. An impact resistant structure of a helicopter according to claim 1, further comprising
a plurality of curved panels, for taking a horizontal load and which are adapted to
crush in a parallelogram shape due to a vertical load in the event of a crash, the
curved panels being arranged substantially in a longitudinal direction of said helicopter
and connected to a sub-floor outer skin or web of said helicopter.
3. An impact resistant structure of a helicopter according to claim 2, further comprising
a truss frame connecting said curved panels substantially in an X-shape so as to function
as a frame member for holding said curved panels during a normal operational use but
not preventing said curved panels from deforming to said parallelograph shape in the
event of a crash.
4. An impact resistant structure of a helicopter according to claim 2, wherein a floor
beam of said helicopter is arranged on said curved panels, said floor beam being connected
to said frame to which said energy absorber is directly connected, whereby a frame-floor
beam structure is formed.
5. An impact resistant structure of a helicopter according to claim 4, wherein a cabin
structure is positioned above said frame-floor beam structure, said cabin structure
being connected to said frame at both side ends of said frame.
6. An energy absorber comprising: a plurality of independent hollow tubes of fiber reinforced
composite material integrally formed by bundling only said hollow tubes of fiber reinforced
composite material, said hollow tubes of fiber reinforced composite material being
arranged so as to minimise the number of intersecting walls of said hollow tubes of
fiber reinforced composite material.
7. An energy absorber comprising: a plurality of independent hollow tubes of fiber reinforced
composite material bundled by an outer layer of fiber reinforced composite material,
wherein said hollow tubes of fiber reinforced composite material and said outer
layer of fiber reinforced composite material are arranged so as to minimise the number
of intersecting walls of said hollow tubes of fiber reinforced composite material
or outer layer of fiber reinforced composite material.
8. An energy absorber according to claim 7, wherein said hollow tubes of fiber reinforced
composite material and said outer layer of fiber reinforced composite material are
arranged such that the number of intersecting said walls of said hollow tubes or outer
layer is less than four.
9. An energy absorber according to claim 6, 7 or 8, wherein said hollow tubes of fiber
reinforced composite material and/or said outer layer of fiber reinforced composite
material for bundling said hollow tubes are formed in a plurality of layers, a film-shaped
layer material having lower strength than that of a base material being inserted between
end portions of said layers.
10. An energy absorber according to claim 7, 8 or 9, wherein said hollow tubes of fiber
reinforced composite material and said outer layer of fiber reinforced composite material
for bundling said hollow tubes are integrally formed.
11. An energy absorber according to any of claims 6 to 10, wherein a foaming material
is inserted into a space between said hollow tubes of fiber reinforced composite material,
and/or in a space between said hollow tubes of fiber reinforced composite material
and said outer layer of fiber reinforced composite material, and/or a space inside
said hollow tubes of fiber reinforced composite material.
12. An energy absorber according to any of claims 6 to 11, wherein said hollow tubes of
fiber reinforced composite material are provided with internal space for holding small
pieces generated by progressive crushing in the event of a crash.
13. An energy absorber according to any of claims 6 to 12, wherein the cross-sectional
shape of each of said hollow tubes of fiber reinforced composite material is circular,
elliptic, square, triangular, hexagonal, or octagonal.
14. An energy absorber according to claim 7, wherein said hollow tubes of fiber reinforced
composite material are arranged in a row or in plural rows and are bundled circularly,
elliptically, rectangularly, or squarely by said outer layer of fiber reinforced composite
material.
15. An energy absorber according to claim 11, wherein said hollow tubes of fiber reinforced
composite material, said foaming material, and said outer layer of fiber reinforced
composite material are integrally formed.
16. An impact resistant structure of a helicopter, comprising: an energy absorber positioned
under a floor of said helicopter and directly connected to a cabin frame of said helicopter,
said energy absorber being arranged in accordance with the distribution of ground
reaction forces on a general ground surface in the event of a crash.